1. Field of the Invention
The present invention relates to a variable valve apparatus of an internal combustion engine for making a phase of driving and a lift amount of an intake or an exhaust valve variable.
2. Description of the Related Art
An engine which is an internal combustion engine mounted to an automobile is mounted with a variable valve apparatus for changing opening and closing timings constituting a phase of driving an intake/exhaust valve and a lift amount thereof in accordance with an operation state of the automobile for reason of a countermeasure against emission gas of the engine, a reduction in fuel cost or the like.
There is such a variable valve apparatus in which a moving displacement at a base section and a lift section of a cam face of a drive cam integrally formed with a cam shaft is converted to a displacement in a rocking cam moving direction of a rocking cam face in which a base section and a lift section are continuous. According to rocking cams used in such a variable valve apparatus, in many cases, a region at which the rocking cam face at a rocking end and a rocker arm roller on a side of a rocker arm are made to be able to be adjusted variably by shifting a rocking range of the rocking cam by driving a fulcrum moving mechanism in a rocker arm mechanism.
In this case, opening/closing timings constituting a mode of driving an intake or an exhaust valve and a lift amount thereof are adjusted by shifting a lift section rate at which the base section and the lift section constituting the rocking cam face and the rocker arm roller are opposed to each other in accordance with the operation state of the automobile.
As an example thereof, there is a rocker arm mechanism including a variable axially supporting member which is switched to vary by a drive source, a middle arm a fulcrum side of which is axially supported by the variable axially supporting member and a rocking side of which is rocked by being brought into contact with the drive cam, and the rocking cam a fulcrum side of which is axially supported by the supporting shaft and which is rocked by receiving a press force from the middle arm being proximate thereto by an input point for pressing the rocker arm roller on a side of the rocker arm by the rocking cam face at the rocking end. By operating to switch the variable axially supporting member in the rocker arm mechanism, a drive cam opposed roller of the middle arm is moved frontward/rearward in a direction of rotating the drive cam, thereby, a lift section of the middle arm is displaced. That is, the input point of the opening/closing operating force of the middle arm to the rocking cam is changed in a lift direction, in corporation therewith, a rocking region in which the rocker arm roller on the side of the rocker arm is opposed to the lift section on the rocking cam face for transmitting the opening/closing operating force is changed. In this way, the rocker arm mechanism adjusts the opening/closing timings and the lift amount constituting the mode of driving the intake or the exhaust valve moved in corporation with the rocker arm by operating to move the drive cam opposed roller in the direction of rotating the drive cam.
FIG. 9 shows an example of a displacement diagram showing an amount of operating a driven member driven by the drive cam of the rocker arm mechanism.
Here, a bold line CH1 shows a diagram showing an amount of operating the driven member when the drive cam opposed roller of the middle arm is shifted to a delay side constituting the direction of rotating the drive cam by operating the variable axially supporting member of the rocker arm mechanism. Further, a broken line CH2 shows a diagram showing the amount of operating the driven member when the drive cam opposed roller of the middle arm is shifted relative to the bold line CH1 by an advance amount R0 on an advance side (left side of FIG. 9) constituting a direction reverse to the direction of rotating the drive cam. By displacing to advance/delay the driven cam opposed roller on the side of the middle arm in the direction of rotating the drive cam in accordance with the operation of the variable axially supporting member, a maximum position of operation of the driven member can be shifted by R0. Further, by making the input point of the middle arm brought into contact with the rocking cam changeable, an amount of operating a lift height of the intake of the exhaust valve can be reduced to h2 by changing the rocking range of the rocking cam and preventing a predetermined cam height of the drive cam from being operated to the intake or the exhaust valve. Therefore, lift amount displacement regions E1, E2 of the intake or the exhaust valve moved in corporation with the rocker arm are shifted from each other and an amount h1, h2 operating a lift start point e1 and a lift finish point e2 and the lift height is changed to increase/decrease.
Incidentally, there is a variable valve apparatus for shifting a rate of making a rocker arm roller on a side of a rocker arm opposed to a base section and a lift section on a rocking cam face of a rocking cam (refer to JP-A-2003-239712).
Meanwhile, as is apparent from the cam lift amount displacement diagram shown in FIG. 9, by a difference in the advance amount R0 or a cam shape, widths of a change region ea of the lift start point e1 and a change region eb of the lift finish point e2 in a crank angle direction are respectively changed.
Here, the width eb of the change region of the lift finish point e2 corresponds to a control width of the valve opening/closing timings by the rocker arm mechanism. The larger the width eb of the change region of the lift finish point e2, the easier the valve closing control to increase a variable response of a valve closing timing. Particularly, in the case of the intake valve, by making an output control easy by making the valve closing timing related to a charging efficiency variable considerably, it is regarded to be effective in view of a valve closing control to increase the width eb of the change region of the lift finish point e2.